1. Field of the Invention
The present invention relates to structured materials and particles and to methods of making and using them. These particles have application in the release of one or more materials into selected environments and in the absorption of one or more materials from selected environments.
2. Background of the Invention
It is desirable to provide a system for solubilizing poorly-soluble compounds, and to effectively formulate poorly-absorbed compounds whether water-soluble or not, particularly those compounds having pharmacological activity, for controlled release into, or absorption from, various environments, particularly aqueous environments.
A number of challenges to this task have not been met by existing methods of formulation. Particularly in a pharmaceutical or nutriceutical application, it is not always enough to solubilize the active or drug, even if it is in a non-toxic vehicle; the vehicle must lend itself to whatever transformation—e.g., encapsulation, granulation, enteric coating, compaction, freeze- or spray-drying—is required to arrive at the correct delivery format. For example, for pharmaceutical actives (medicaments) where the most desirable format is the pill form for oral delivery, still the most common and desirable drug format by far, most liquid solvents and even surfactant-rich phases, unless encapsulated, will often be incompatible with the simplest tablet manufacturing procedures, since these procedures were generally developed with solids and powders in mind. Yet the application of these procedures to poorly-soluble drugs, or even to drugs of moderate or high solubility, without the use of liquids or surfactants often yields a pill that achieves only a very limited bioavailability when administered. It should also be pointed out that while acidic (e.g., hydrochloride) or basic (e.g., sodium) salt forms of low-solubility drugs can often be soluble, such salts can precipitate in the body when they encounter pH conditions that deprotonate the acidic salt or protonate the basic salt.
For actives that are to be delivered by injection, solubilization of such compounds is made challenging by the very limited selection of solvents and structured liquids that are approved for injection at levels that would be required to solubilize the drug. Furthermore, water-miscible liquid excipients, e.g., ethanol, are by themselves of limited value since, even when the drug is soluble in neat ethanol, it will often precipitate upon contact with water, either diluent water for injection or in the aqueous milieu of body fluids, such as blood. In fact any (unencapsulated) delivery system containing a crucial matrix component having appreciable water solubility could partially or fully disintegrate prematurely in an aqueous environment, and lead to precipitation and/or poor absorption of the active compound.
Furthermore, delivery systems that rely on solubilization of actives in surfactant-rich (e.g., polar lipid-rich) phases, such as liposomes and lyotropic liquid crystals and liquids, are sometimes unable to solubilize appreciable loadings of active because the aliphatic chains can be incompatible with polar groups on the active compound; a great many pharmaceutical actives with low water solubility contain polar groups, in fact often 4 or more polar groups. Low drug loadings are problematic because in order to deliver a therapeutic amount of drug, large quantities of excipients must be given, increasing overall toxicity of the formulation, and often promoting low patient compliance if large, unpleasant dosage forms result; this is particularly problematic for vehicles that are themselves not well-absorbed, or do not enhance the absorption of the drug beyond the inherent enhancement due to solubilization. The particles of Landh and Larsson (U.S. Pat. No. 5,531,925) suffer from this limitation, particularly for poorly-soluble drugs but also to some extent in the case of water-soluble drugs and biopharmaceuticals (proteins, nucleic acids, and other high-MW actives). And liposomes based on lipid- or surfactant-based lamellar phases (lamellar liquid crystalline and lamellar crystalline phases) suffer from a number of well-known drawbacks and limitations, most notably unfavorable interactions with biomembranes that limit their ability to deliver their payload to cells, instability in the GI tract, lack of controllable porosity or fusogenicity, and shelf-life limitations, as well as their overall lack of success in solubilizing drugs and actives of low water solubility, making them of limited utility for both water-soluble and poorly-soluble actives. Emulsions in which lipid or surfactant monolayers, multilayers, lamellar liquid crystalline domains or lamellar crystalline domains stabilize droplets of one fluid in another similarly suffer from unfavorable interactions with biomembranes, lack of integrity particularly in the GI tract, somewhat low payload levels, poor suitability for targeting, and shelf-life limitations, and are not well suited for processing into forms that are compatible with solids-based formulations. And emulsions or droplet systems in which each droplet is surrounded by a plurality of particles of another material, all undergoing independent diffusion around the droplet (and frequently separated from one another by liquid intervening or stabilizing layers), may show good stability, but suffer from gaps between the particles that compromise the ability of the material to control the egress of active out of, or ingress of confounding factors into, the droplet.